1. Field of the Invention
The present invention relates to a rear (inclusive of rear-side or diagonal rear) monitoring system, and more particularly to a rear monitoring system for picking up the road image on the rear of one""s own vehicle by an image pick-up means such as a video camera installed on the vehicle such as a motor car, detecting another vehicle approaching from the diagonal-rear direction of one""s own running vehicle using the road image picked up and giving a warning to a driver.
2. Description of the Related Art
For example, when a driver of a vehicle running on one-side two lanes of e.g. a speed way intends to change his own vehicle lane, if he changes the lane while he misses another vehicle which catches up with his own vehicle on another lane at a higher speed than his own vehicle from the diagonal-rear direction, there is strong possibility of a serious accident. Therefore, it is desired that the driver surely notices or recognizes other vehicles in the environment.
When another following vehicle on the same lane abruptly approaches his own vehicle from the rear, if the driver of his own vehicle makes abrupt braking, there is possibility of bumping-into-the back.
When another vehicle runs forward on the same lane at a lower speed than that of his own vehicle, if a driver dozes, there is a danger of bumping-into-the back.
A technique for avoiding the danger as described above has been proposed as an environment monitoring system for a vehicle disclosed in JP-A-7-50769. Now referring to FIGS. 11A-11D, an explanation will be given of this environment monitoring system.
FIGS. 11A-11C are views for explaining a change in a rear background image acquired by a video camera 1. FIG. 11A shows a status inclusive of one""s own vehicle. FIG. 11B shows an image picked up by a video camera 1 at timing t in an environment of one""s own vehicle. FIG. 11C shows an image picked up at timing t+xcex94t.
Now it is assumed that one""s own vehicle is running straight on a flat road. The road sign and building residing in the rear of one""s own vehicle in FIG. 11A are observed as images shown in FIG. 11B and 11C at timings t and t+xcex94t, respectively. Coupling the corresponding points in these two images provides speed vectors as shown in FIG. 11D. These are referred to as xe2x80x9coptical flowsxe2x80x9d. Where a following vehicle approaches, the directions of the vectors in the optical flows in FIG. 11D are contrary. Using the optical flows, the conventional environment monitoring system monitors the relationship between one""s own vehicle and the following vehicle or another vehicle running on an adjacent lane to detect the other vehicle approaching one""s own vehicle, thereby giving a warning to a driver.
In some prior arts, a technique of searching corresponding points using two cameras is adopted. Specifically, an edge point Pa of an object is detected from a luminance difference between the adjacent pixels on the image picked up by a camera. A point Pb of the image picked up by another camera corresponding to the detected edge point is detected. The position of another approaching vehicle is acquired by the pixel coordinates of Pa and Pb. On the basis of the position acquired, the pertinent driver is given a warning of the existence of another vehicle approaching his own vehicle.
Further, there is a conventional technique of detecting the location of a detected other vehicle in such a manner that the road image on a straight speed way having one-side three lanes as shown in FIG. 12 is image-processed to detect the white lines (each of which is a lane-dividing line such as a white line, yellow line, white broken line, etc., and hereinafter referred to as xe2x80x9cwhite linexe2x80x9d) of the lane on which one""s own vehicle is running so that one""s own lane is discriminated from the adjacent lane and any other vehicle is detected for each monitoring lane so that it is decided whether the detected vehicle is located on the one""s own lane or the other adjacent lane. In some applications, the monitoring area is defined in order to save the processing time for the lane which is not required for monitoring.
Meanwhile, the prior art detects white lines by a technique of image processing. However, it was very difficult to detect the white lines by image-processing the road image with low contrast which is created in the night time and the event of rain. In order to obviate such an inconvenience, it can be proposed to pick up the white lines by a camera while the rear of vehicle is projected with light. However, the glare of light may obstruct the safe running of the following vehicle so that it is dangerous to project light to a far distance. In addition, it takes a relatively long time for processing to detect the white lines. Therefore, even if the road image has a high contrast, the white lines cannot be easily detected.
An object of the present invention is to provide a rear monitoring system for a vehicle which can easily detect white lines for discriminating one""s own lane from an adjacent lane.
In order to attain the above object, in accordance with the present invention, as shown in a basic arrangement view of FIG. 1A, there is provided a diagonal-rear monitoring system for a vehicle for monitoring a relationship between one""s own vehicle and another vehicle comprising:
image pick-up means 10 attached to one""s own vehicle for picking up a diagonal-rear road behind one""s own vehicle to acquire an diagonal-rear road image;
detection means 31a for detecting another vehicle on the basis of the diagonal-rear road image acquired by the image pick-up means;
information acquisition means 31b for acquiring information on a road on which one""s own vehicle has run;
white-line estimating means 31c for estimating white lines on the diagonal-rear road image which distinguish one""s own lane from both adjacent lanes on the basis of the information acquired by the information acquisition means, wherein using the white lines thus estimated, it is decided whether another detected vehicle is located on one""s own lane or the adjacent lanes.
In this configuration, in the nighttime when the white lines cannot be detected from the diagonal-rear road image, the white lines on the diagonal-rear road image can be estimated using the information on the road on which one""s own vehicle has run.
Preferably, the information acquisition means comprises:
front image pick-up means 61 attached to one""s own vehicle for picking up a front road ahead of one""s own vehicle to acquire an diagonal-rear road image; and
white-line information acquisition means 62 for successively acquiring information on white lines which distinguish one""s own lane from both adjacent lanes on the basis of the front road image acquired by the front image pick-up means; and
the white line estimating means estimates white lines on the diagonal-rear road image which distinguish one""s own lane from both adjacent lanes on the basis of the information acquired by the white-line information acquisition means.
In this configuration, by only acquiring the front image, the white lines can be estimated.
Preferably, the diagonal-from image pick-up means and the white-line information acquisition means are those originally installed in the system.
In this configuration, it is not necessary to provide the front image pick-up means and white-line information acquisition means separately.
Preferably, the information acquisition means comprises position information acquisition means 31b-1 for acquiring vehicle position information indicative of a position coordinate of a vehicle at a prescribed period when the vehicle is running on one""s own lane, the position information varying according to a helm angle and running speed of the vehicle, and
the white-line estimating means estimates white lines on the diagonal-rear road image which distinguish one""s own lane from both adjacent lanes on the basis of the information acquired by the position information acquisition means.
In this configuration, the white lines can be easily estimated by only acquiring the vehicle position information on the basis of the helm angle and running speed.
In accordance with the present invention, as shown in FIG. 1B, there is provided a diagonal-rear monitoring system for a vehicle for monitoring a relationship between one""s own vehicle and another vehicle comprising:
image pick-up means 10 attached to one""s own vehicle for picking up a diagonal-rear road behind one""s own vehicle to acquire an diagonal-rear road image;
detection means 31a for detecting another vehicle on the basis of the diagonal-rear road image acquired by the image pick-up means;
map storage means 74 for storing road information inclusive of a road shape;
information acquisition means 72 for acquiring information of a present location of one""s own vehicle;
white-line estimating means 31c for reading the road information behind the present location of one""s own vehicle on the basis of the information acquired by the information acquisition means and estimating white lines on the diagonal-rear road image which distinguish one""s own lane from both adjacent lanes on the basis of the road information thus read, wherein using the white lines thus estimated, it is decided whether another detected vehicle is located on one""s own lane or the adjacent lanes.
In this configuration, the white lines on the diagonal-rear road image can be easily estimated using the road information.
Preferably, the map storage means and the information acquisition means are those of a GPS navigation device originally installed to inform a driver of a present location of one""s own vehicle on a map on a display.
In this configuration, it is not necessary to the map storage means and the information acquisition means separately.
In accordance with the present invention, as shown in FIG. 1B, there is provided a diagonal-rear monitoring system for a vehicle for monitoring a relationship between one""s own vehicle and another following vehicle using an optical flow comprising:
image pick-up means 10 attached to one""s own vehicle for picking up a diagonal-rear road behind one""s own vehicle to acquire diagonal-rear road images at a prescribed period;
optical-flow detection means 31d for detecting the optical flow generated from another vehicle on the basis of two successive road images acquired by the image pick-up means;
information acquisition means 72 for acquiring information on a road on which one""s own vehicle has run;
white-line estimating means 74 for estimating white lines on the diagonal-rear road image which distinguish one""s own lane from both adjacent lanes on the basis of the information acquired by the information acquisition means, wherein using the white lines thus estimated, it is decided whether another vehicle generating the detected optical flow is located on one""s own lane or the adjacent lanes.
In this configuration, in the nighttime while the white lines cannot be detected from the diagonal-rear road image, they can be estimated on the basis of the road on which one""s own vehicle has run.
In accordance with the present invention, as shown in FIG. 1B, there is provided a diagonal-rear monitoring system for a vehicle for monitoring a relationship between one""s own vehicle and another following vehicle using an optical flow comprising:
image pick-up means 10 attached to one""s own vehicle for picking up a diagonal-rear road behind one""s own vehicle to acquire diagonal-rear road images at a prescribed period;
optical-flow detection means 31d for detecting the optical flow generated from another vehicle on the basis of two successive road images acquired by the image pick-up means;
map storage means 74 for storing road information inclusive of a road shape;
information acquisition means 72 for acquiring information of a present location of one""s own vehicle;
white-line estimating means 31c for reading the road information behind the present location of one""s own vehicle on the basis of the information acquired by the information acquisition means and estimating white lines on the diagonal-rear road image which distinguish one""s own lane from both adjacent lanes on the basis of the road information thus read, wherein using the white lines thus estimated, it is decided whether another vehicle generating the detected optical flow is located on one""s own lane or the adjacent lanes.
In this configuration, since the white lines can be estimated on the basis of the road information, the white lines on the diagonal-rear road image can be easily estimated through acquisition of the road image.
In accordance with the present invention, as shown in FIG. 1C, there is provided a diagonal-rear monitoring system for a vehicle for monitoring a relationship between one""s own vehicle and another vehicle comprising:
image pick-up means 10 attached to one""s own vehicle for picking up a diagonal-rear road behind one""s own vehicle to acquire an diagonal-rear road image;
detection means 31a for detecting another vehicle on the basis of the diagonal-rear road image acquired by the image pick-up means;
white-line retrieval region setting means 31e for setting a retrieval region within which white lines for distinguishing one""s own lane from both adjacent lanes are to be retrieved on the diagonal-rear road image picked up by the image pick-up means; and
white-line detection means 31f for retrieving the retrieval region to detect the white lines, wherein using the white lines thus detected, it is decided whether another detected vehicle is located on one""s own lane or the adjacent lanes.
Preferably, the retrieval region is set using white-line information acquired on the basis of a front image pick-up in a front monitoring device originally.
In this configuration, the white lines can be detected through the retrieval of only the retrieval region set by the the retrieval region setting means 31e. 
The above and other objects and features of the present invention will be more apparent from the following description taken in conjunction with the accompanying drawings.